Differences in ABA synthesis and physiological and biochemical responses of seedlings of different maize varieties under osmotic stress

Osmotic stress significantly inhibited the growth and biomass accumulation of both aboveground and belowground parts in seedlings of different maize cultivars, and reduced the relative water content (RWC) of the plants. Specifically, the aboveground and root biomass of Zhengdan 958, Nongda 3138, and Nongda 364 were reduced by 32.8% and 5.9%, 37.1% and 10.5%, and 43.8% and 20.1%, respectively. Meanwhile, drought stress markedly upregulated the expression of key ABA biosynthesis genes—including ZmNCED1, ZmAO2, and ZmABA3—in both leaves and roots across cultivars. Among them, Zhengdan 958 exhibited the greatest increase, with transcript levels rising 1.5- to 12.9-fold compared to the control, whereas Nongda 364 showed the smallest increase, ranging from 0.4- to 1.3-fold. Osmotic stress also enhanced the activity of aldehyde oxidase, a key enzyme in ABA biosynthesis, thereby promoting ABA accumulation. Among the cultivars, Nongda 364 exhibited the smallest ABA increase in leaves and roots (140% and 90%, respectively), while Zhengdan 958 showed the largest. In addition, osmotic stress significantly elevated the activities of antioxidant enzymes in maize, including POD, SOD, and CAT, with the degree of increase consistent with the trend of ABA accumulation among cultivars. A comprehensive analysis of plant growth, physiological and biochemical characteristics related to ABA biosynthesis and accumulation, and antioxidant enzyme activities under osmotic stress revealed that drought tolerance among the cultivars followed the order: Zhengdan 958 > Nongda 3138 > Nongda 364. These findings elucidate the role of ABA in mediating maize responses to osmotic stress in cultivars with varying drought tolerance and provide a theoretical foundation for breeding drought-tolerant cultivars and developing stress-resilient cultivation strategies.